I'm traveling in India at the moment and have an anecdote I'd like to share.
I often get religious visitors on this site asking sarcastically where all of the "atheist charities" are. I try to explain to them that it seems silly to me to start an explicitly atheist charity, as I cannot see the purpose. Besides alienating a good deal of the population, there is as much reason to start an atheist charity as there is to start a charity for people who don't believe in the Loch Ness Monster. I then try to explain that there are many non-religious charities in the world, which we refer to as secular charities. Some of the world's biggest and most well-known charities belong to this category, such as the Red Cross, UNICEF, Doctors Without Borders, the World Wildlife Fund, etc. It's also worth noting that the largest giving team on Kiva.org is the Atheist team, with the Christian team a distant second place. I've written about this topic of charities before.
So I just met an Indian lady who runs a charity which is doing work that I feel is critical to the future of India both economically and environmentally. I won't explicitly identify the charity or its work, in order to protect the innocent. She is a lady who volunteers her time selflessly and who is passionate about the work she is doing to help improve and preserve her country. She confessed to me that she is an atheist, and her two partners in running the charity are also atheists. I was immediately intrigued by this admission of atheism by members of a society which I had considered to be one of the most religious on the planet. I asked her if she was able to freely express this to her own society, and she said she could not. She told me that Indian people don't like people who don't pray, and her two partners fake religious belief in public by participating in prayers. She told me that it could be dangerous both to herself and to her work if she was identified publicly as a non-believer.
Another interesting point is that despite being non-religious, this lady uses religion to further the goals of her charity. She works with some of the most uneducated people in the world. I'm talking about the kind of people who have no schools in their villages and who know very little of the world outside of those villages. So she uses one thing these people do know, their religious myths, to relate to them and to put the charity's work into terms that they can understand. She pretends to share their beliefs in order for her charity to function.
One can never tell just how many atheists there are in a society which will punish lack of belief. And those atheists are capable of doing good work just because they care. I care too, and I have just become a significant donor to this particular charity.